NASA Administrator Charles Bolden will speak with astronaut Dottie Metcalf-Lindenburger, commander of the 16th NASA Extreme Environment Mission Operations (NEEMO) mission, and her fellow crewmate Timothy Peake of the European Space Agency at 4:10 p.m. EDT Wednesday, June 20 as they perform their final "spacewalk" of the mission, 63 feet below the ocean's surface.

The administrator's call to the crew will air live on NASA Television.

The NEEMO 16 crew has been simulating asteroid exploration on the ocean floor since June 11. They are scheduled to return to the surface June 22, after living for 12 days inside the National Oceanic and Atmospheric Administration's Aquarius Underwater Laboratory off the coast of Key Largo, Fla. At the successful completion of the mission, they will have performed 16 underwater spacewalks.

The NEEMO 16 mission is focusing on three particular challenges of an asteroid mission. The crew is investigating communication delays, restraint and translation techniques and optimum crew size. The isolation and microgravity environment of the ocean floor allows the NEEMO 16 crew to study and test concepts for how future exploration of asteroids could be conducted.

Metcalf-Lindenburger and Peake are accompanied inside Aquarius by Kimiya Yui of the Japan Aerospace Exploration Agency and Steven Squyres of Cornell University. Squyres also was a member of NEEMO 15.